The present application relates to a memory and a write control method that are configured by a memory layer storing the magnetization state of a magnetic body as data and a magnetization fixed layer whose direction of magnetization is fixed and that store data in a memory device by changing the direction of magnetization of the memory layer by allowing a current to flow in the stacked direction.
In related art, as the use of information communication devices, especially, miniaturized electronic devices used particularly in mobile terminals and the like become widespread, it is desirable for devices such as memories or logic circuits configuring the electronic devices to have improved performance such as high-density integration, high operation speed, low power consumption, or the like.
In such electronic devices, non-volatile memories are considered to be major components used for improving the functions of the electronic devices. As the non-volatile memory, a semiconductor flash memory, a FeRAM (Ferroelectric non-volatile memory), and the like have been practically implemented, and researches and developments for further improving the performance thereof are being actively undertaken.
Recently, as new non-volatile memories each using a magnetic body, the development of MRAMs (Magnetic Random Access Memories) utilizing a tunnel magnetoresistive effect has advanced markedly. Relating to the MRAMs, for example, a technology disclosed in J. Nahas et al., IEEE/ISSCC 2004 Visulas Supplement, p. 22 and the like has attracted attention.
In the MRAM, tiny memory devices storing data are regularly disposed and are wired such that each of the tiny memory devices can be accessed. The wires have a structure in which, for example, word lines and bit lines are disposed. Each memory device is configured to include a memory layer storing data as the direction of magnetization of a ferromagnetic body.
As memory devices, magnetic memory devices employing a structure utilizing a so-called magnetic tunnel junction (MTJ) are used. The magnetic tunnel junction is configured by the above-described memory layer, a tunnel insulating layer (nonmagnetic spacer film), and a magnetization fixed layer whose direction of magnetization is fixed. For example, the direction of magnetization of the magnetization fixed layer can be fixed by disposing an antiferromagnetic layer.
In such a structure, a so-called tunnel magnetoresistive effect that changes a resistance value for a tunnel current flowing through the tunnel insulating layer in accordance with an angle formed by the direction of magnetization of the memory layer and the direction of magnetization of the magnetization fixed layer occurs. Accordingly, data can be read out by using the tunnel magnetoresistive effect. The resistance value has a maximum value when the magnetization directions of the memory layer and the magnetization fixed layer are antiparallel to each other. On the other hand, the resistance value has a minimum value when the magnetization directions of the memory layer and the magnetization fixed layer are parallel to each other.
In related art, as a method of storing data (hereinafter, it may be abbreviated as “data writing” or “write”) by writing data into a memory device, for example, a technology utilizing asteroid characteristics is disclosed in JP-A-10-116490. In addition, a technology utilizing switching characteristics is disclosed in U.S. Patent Application Publication No. 2003/0072174.
In particular, the writing of data into a memory device is performed as follows. In other words, data is written by controlling the magnetization direction of the memory layer of the memory device in accordance with a synthetic current magnetic field that is generated by allowing currents to flow through both a word line and a bit line that are disposed to the upper and lower sides of the memory device and are disposed to be perpendicular to each other. Generally, a difference in the magnetization directions at the time of writing data is written into the memory device in correspondence with data “0” and data “1”.
On the other hand, a method of reading out data (hereinafter, it may be abbreviated as “reading out data” or “read”) from the memory device 2 is performed as follows. A memory cell is selected by using a device such as a transistor, and a difference in the magnetization directions of the memory layer is detected as a difference in a voltage signal by utilizing the tunnel magnetoresistive effect of the memory device. Accordingly, the written data can be detected.
In the MRAM, data “0” and data “1” are written by reversing the magnetization direction of the memory layer that is configured by a ferromagnetic body. Accordingly, when the MRAM is compared to other non-volatile memories, the best feature of the MRAM is that data rewriting can be performed an almost unlimited number of times (for example, 1015 times) at a high speed.
However, in the MRAM, in order to rewrite the data written once, it is necessary to generate a relatively large current of a degree (for example, several mA to several tens of mA) for an address wire. In such a case, the power consumption becomes high.
In addition, in the MRAM, an address wire for writing and an address wire for reading are used for each memory device. Accordingly, it is difficult to structurally miniaturize the memory cell.
In addition, the address wires become thin in accordance with miniaturization of the memory device. Accordingly, it is difficult to allow a sufficient current to flow, and coercivity increases. Therefore, there are cases where a necessary current magnetic field is increased and the power consumption increases. As a result, it is difficult to miniaturize the memory device.
Thus, in order to solve the above-described problems, technologies for writing data into a memory device without using a current magnetic field have been researched. In particular, in order to implement a configuration in which magnetization reversal can be performed by using a relatively low current, memories that are configured so as to utilize magnetization reversal caused by a spin transfer as described in U.S. Pat. No. 5,695,864 have attracted attention.
Here, in JP-A-2003-17782, magnetization reversal caused by a spin transfer is described. The magnetic inversion caused by spin transfer is to generate magnetization reversal in a magnetic body by injecting spin-polarized electrons passing through the inside of another magnetic body into the magnetic body.
According to this phenomenon, when the spin-polarized electrons passing through a magnetic layer (magnetization fixed layer) whose direction of magnetization is fixed are moved into a different magnetic layer whose direction of magnetization is not fixed, torque is applied to magnetization of the different magnetic layer (magnetization free layer). Then, by allowing a current having a predetermined threshold value or higher to flow through the different magnetic body, the direction of magnetization of the magnetic layer can be inverted.
For example, a current is allowed to flow through a giant magnetoresistive effect device (GMR device: Giant Magneto Resistive Head) or a magnetic tunnel junction device (MTJ device) that has a magnetization fixed layer and a magnetization free layer in a direction perpendicular to the layer faces. Accordingly, the direction of magnetization of at least a part of the magnetic layer of the device can be reversed.
Then, a memory device having a magnetization fixed layer and a magnetization free layer (memory layer) is configured, and by changing the polarity of a current flowing through the memory device, the magnetization direction of the memory layer is reversed, whereby rewriting for a shift from data “0” to data “1” and a shift from data “1” to data “0” is performed.
On the other hand, in the reading out of written data, by using a configuration in which a tunnel insulating layer is disposed between the magnetization fixed layer and the magnetization free layer (memory layer), similarly to the MRAM, the tunnel magnetoresistive effect can be utilized.
The magnetization reversal caused by a spin transfer has an advantage in that magnetization reversal can be achieved without increasing the current even in a case where the memory device is miniaturized.
For example, the absolute value of the current flowing through the memory device for magnetization reversal is equal to or smaller than 1 mA for a memory device having a scale of about 0.1 μm. In addition, since the absolute value of the current decreases in proportion to the volume of the memory device, scaling up is advantageous. In addition, the word line for storage, which is disposed in the MRAM, is not necessary. Accordingly, there is an advantage in that the configuration of the memory cell is simplified.
In the description below, a memory device using a spin transfer is referred to as a SpRAM (Spin transfer Random Access Memory). In addition, a spin-polarized electron stream that causes the spin transfer is referred to as a spin injection current.
As a non-volatile memory capable of implementing low power consumption and high capacity with the advantages of the MRAM maintained, which includes a high speed operation and an almost unlimited number of times of rewriting, the SpRAM is highly anticipated.
In addition, JP-A-2005-277147 is also an example of related art.